Three-dimensional object production

ABSTRACT

An example apparatus to produce a three-dimensional object comprises a controller, a build area configured to receive a layer of particulate material, a printhead, and an ultraviolet light emitting diode energy source. The controller is to cause the printhead to deposit a liquid which absorbs ultraviolet radiation onto the layer of particulate material. The controller is further to cause the ultraviolet light emitting diode energy source to irradiate the liquid, after the liquid has been deposited onto the layer of particulate material, thereby to heat the liquid and cause a portion of the particulate material to solidify.

Apparatus that generate three-dimensional objects, including thosecommonly referred to as “3D printers”, provide a convenient way toproduce three-dimensional objects. These apparatus typically receive adefinition of the three-dimensional object in the form of an objectmodel. This object model is processed to instruct the apparatus toproduce the object using a particulate material or plural particulatematerials. This may be performed on a layer-by-layer basis. Generatingobjects in three-dimensions presents many challenges that are notpresent with two-dimensional print apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features of the present disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate features of the presentdisclosure, and wherein:

FIG. 1 is a diagram of a three-dimensional printing apparatus accordingto an example;

FIG. 2 is a diagram of a three-dimensional printing apparatus accordingto a second example;

FIG. 3 is a diagram of a three-dimensional printing apparatus accordingto a third example;

FIG. 4 is a diagram of a three-dimensional printing apparatus accordingto a fourth example;

FIG. 5 is a diagram of a three-dimensional printing apparatus accordingto a fifth example;

FIG. 6 shows absorption spectra of particulate material and liquidsaccording to an example;

FIG. 7 shows absorption spectra of inks according to an example;

FIG. 8 shows a method of producing a three-dimensional object accordingto an example;

FIG. 9 shows a diagrammatic representation of an example set ofcomputer-readable instructions within a non-transitory computer-readablestorage medium.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousspecific details of certain examples are set forth. Reference in thespecification to “an example” or similar language means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least that one example, but notnecessarily in other examples.

As described herein, an example apparatus to produce a three-dimensional(3D) object comprises a printhead configured to deposit a liquid whichabsorbs ultraviolet radiation onto a layer of particulate material, andan ultraviolet light emitting diode energy source (UV-LED) to emitelectromagnetic energy having a maximum intensity at a wavelengthbetween about 200 nm to about 405 nm. In some examples the apparatusfurther comprises a controller to cause the printhead and UV-LED energysource to perform their functions. The UV-LED energy source is toirradiate the layer of particulate matter with a substantially uniformintensity across the layer, after the liquid has been deposited onto thelayer of particulate material, thereby to heat the liquid and cause aportion of the particulate material to solidify. Irradiating the layermeans that the liquid is also irradiated. As the liquid, or one or morecomponents of the liquid, absorb the ultraviolet (UV) electromagneticenergy/radiation emitted by the UV-LED energy source, the temperature ofthe liquid increases. Heat from the liquid is transmitted, for exampleby conduction, to particulate material in the vicinity of the liquid.The temperature of the particulate material in the vicinity of theliquid therefore also increases. If the temperature of the particulatematerial in the vicinity of the liquid reaches a threshold temperature,such as a temperature sufficient for the particulate material to melt orsinter, the particulate material will fuse and solidify as it cools.Accordingly, the three-dimensional object can be built on alayer-by-layer basis. In some examples, the UV-LED energy source is aUV-LED energy source comprising one or more UV-LEDs, for example anarray of UV-LEDs.

UV-LEDs may emit ultraviolet electromagnetic energy having a narrowspectral width. The spectral width is defined as the range ofwavelengths surrounding a peak wavelength, at a power level greater thanor equal to half the maximum power level. Thus, the majority of thepower emitted by energy source will be within the range of the spectralwidth. In some examples more than 50%, 60%, 70%, 80% or 90% of the powermay be emitted within this range. The peak wavelength has the maximumintensity and may, for example have a wavelength at the center of thespectral width. Thus, an emitter with a narrow spectral width may emitelectromagnetic radiation that is within a narrow range of a centralpeak wavelength. Such an emitter may be known as a narrowband emitter,and may have a spectral width of about 5 nm to about 50 nm. In contrast,a lamp energy source, such as a halogen or incandescent type lamp,generally emits electromagnetic radiation having a large spectral width,and may have a spectral width of greater than about 100 nm. In someexamples lamp energy sources have spectral widths of about 1000 nm, andmay have many peaks within the emission spectra. Hence, emissions havinga large spectral width comprise electromagnetic energy spread over awide wavelength range. A lamp may therefore be known as a widebandemitter. A laser, for example, comprises an extremely narrow spectralwidth, and may have a spectral width of less than about 5 nm.

The use of UV-LEDs during three-dimensional object fabrication mayprovide benefits over the use of wideband energy sources currently usedin 3D printing. For example, certain components, such as liquids used in3D printing, may be chosen or designed to absorb electromagnetic energyhaving a particular UV wavelength more effectively than otherelectromagnetic energy having another wavelength, such as Infra-Red(IR). Thus, by using UV-LEDs having a maximum intensity at a wavelengthbetween about 200 nm to about 405 nm, in combination with a liquid whichabsorbs this UV radiation, the energy efficiency of the heating processcan be improved because the wavelength and/or spectral width of the LEDscan be selected to match the absorption characteristics of the liquids.This maximizes the amount of energy that is absorbed by the liquid. Thisis in contrast to conventional systems where wideband energy sources areused. The use of wideband emitting energy sources may beenergy-inefficient because certain wavelengths within the widebandenergy are poorly absorbed.

In some examples the UV-LED energy source emits electromagnetic energyhaving a maximum intensity at a wavelength between about 285 nm to about405 nm. A UV-LED energy source that emits energy within this range arerelatively inexpensive compared to other wavelength LEDs. Such a UV-LEDenergy source also has no UVC regulation issues because they do not emitenergy within the UVC wavelength range of 100-280 nm.

A UV-LED energy source may also have a long lifetime compared to moreconventional energy sources, such as lamps. Furthermore, a UV-LED energysource may allow simple DC operation, simple driving control, and/or lowvoltage operation, and have no regulation issues with electromagneticcompatibility (EMC), radio-frequency interference (RFI), and/or highvoltage operation.

A UV-LED energy source may also provide benefits in color 3D printingsystems. For example, IR tends to be poorly absorbed by white and yellowcolored printing agent liquids, such as ink, used in a color 3D printingprocess. It has been found that the use of a UV-LED energy source maycause the printing agent temperature to rise faster than occurs whenusing wideband IR energy sources. If the printing agent is heated at afaster rate, the fusion temperature can be achieved in a shorter time,which reduces the overall time needed to fabricate a 3D object.

It has been found that colored printing agent liquids, such as inks,currently used in color 3D printing have absorption bands within the UVspectrum. Thus, inks already have the ability to absorb energy emittedby the UV-LED energy source and with high efficiency. This can mean thatwhen colored liquids are applied, the particulate material can be fusedwithout the addition of further absorbing liquids, such as dedicated‘fusing’ agents. This effect can be achieved using a UV-LED energysource that emits electromagnetic energy having a maximum intensity at awavelength between about 200 nm to about 405 nm. Specific wavelengths ofthe UV-LED energy source within this range can be selected to ensurethat the energy is absorbed more effectively by the various liquids usedin the printing process. For example, the individual color liquids inthe CMYK inks may each have a different absorption spectrum for UVenergy, so a wavelength may be selected which is absorbed effectivelyacross all the liquids.

Particulate materials used in 3D printing may absorb some UV wavelengthspoorly. For example, build material Polyamide 12 (PA-12) absorbs shortwavelength UV radiation, but poorly absorbs longer wavelength UVradiation. Poor absorbance may be defined as absorbing less than about20% or less than about 10% of incident radiation at the wavelength inquestion. By depositing a liquid which absorbs longer wavelength UVradiation onto the particulate material, and irradiating the layer ofparticulate material with longer wavelength UV radiation, the liquidabsorbs a higher proportion of the UV radiation than the particulatematerial. Thus, LEDs can be selected that have UV emission wavelengthswhich are absorbed less efficiently by the particulate material than theliquid. Thus, any particulate material which has had liquid applied isheated more than particulate material to which no liquid is beenapplied. This can reduce the possibility of the particulate materialsolidifying in places where liquid has not been applied, when exposed toUV radiation.

Accordingly, in some examples the UV-LED energy source emitselectromagnetic energy having a maximum intensity at a wavelengthbetween about 385 nm to about 405 nm. Such wavelengths may be poorlyabsorbed by certain particulate materials, such as PA-12, and may beabsorbed by certain liquids used in 3D printing. Hence, wavelengths maybe selected depending upon the type, or types, of materials and liquidsused in 3D printing. For example, in some examples the liquid may be adye or an ink, and common dyes and inks may readily absorb suchwavelengths. If multiple liquids are being used, a wavelength can beselected which is most effectively absorbed by the liquids.

In one example, the UV-LED energy source wavelength is selected to havea maximum intensity at a wavelength between about 200 nm to about 405nm, and that is greater than 100 nm from an absorbance peak from theparticulate material. In some examples, when the UV-LED energywavelength is offset from an absorbance peak of the particulate materialby at least this amount, the absorbance by the dry particulate materialmay be reduced to levels that prevent melting of the material.

In some examples the UV-LED energy source emits electromagnetic energyhaving a maximum intensity between about 385 and about 395 nm, forexample at a wavelength of about 390 nm. This wavelength may provide agood balance between cost of the LED, and good absorption by liquidsused in printing.

In some examples the UV-LED energy source emits ultravioletelectromagnetic energy having a spectral width of about 5 nm to about 50nm. Hence the UV-LED energy source has a narrow spectral width suitablefor absorption by a number of liquids used in 3D printing systems. Aspectral width within this range can improve absorption efficiency, andtherefore energy efficiency.

In some examples the printhead is a first printhead, and the liquid is afirst liquid, and the apparatus further comprises a second printhead,wherein the controller is to cause the second printhead to deposit asecond liquid which absorbs ultraviolet radiation onto the layer ofparticulate material, after the first printhead deposits the firstliquid. In some examples the first liquid is a dye, and the secondliquid is a pigment-based ink. A dye may be a dye-based ink, whichcomprises a colorant dissolved in liquid, and a pigment-based ink maycomprise a powder of solid colorant suspended in a liquid carrier. Insome examples one or both of the first and second liquids comprise apigment or colorant which gives the liquids color. The pigments orcolorants may be absorbers that cause the liquid to absorb the UVradiation.

In some examples the first liquid deposited by the first printhead iswhite, however in other examples the first liquid is colorless. A whiteliquid may be useful when the particulate material is not white, or whenthe material changes color from white upon solidification. The whiteliquid may be deposited onto the layer of particulate material toprovide a white “base”. Colored liquids may be deposited either directlyon top of this white base, or on a new layer of particulate material.Hence, the second liquid may be colored differently, and may thereforebe deposited liquid to give color to the object. Other colored liquidsmay also be deposited.

In some examples each liquid has a different absorption spectrum withinthe UV wavelength range. Thus a UV radiation wavelength can be selectedfrom within the range of 200 nm to 405 nm, to optimize, increase, and/orbalance absorption of the UV radiation by plural liquids.

As mentioned, a particulate material is selected that has a lowabsorbance level of UV radiation. Thus, the material is heated mosteffectively in regions where a liquid which absorbs UV radiation isdeposited. In examples where the second liquid is colored, theapplication of the first liquid ensures that the particulate material isfused even in regions having a low color density. For example where theapplication of the second liquid is performed at less than 100%coverage, areas which do not have the second liquid may not be heatedsufficiently to melt or fuse and solidify, so the application of thefirst liquid may assist with heating such areas.

In some examples the controller is to cause the UV-LED energy source toirradiate the layer of particulate material, and therefore the firstliquid before the second printhead deposits the second liquid. Thus, theportions of the particulate material comprising the first liquid can bepreheated to almost fusing temperature, without solidifying. In otherexamples, the portions of the particulate comprising the first liquidcan be fully solidified or partially solidified. This may occur inaddition to, or instead of a procedure whereby energy is applied to thelayer of particulate material before any liquids are applied to thelayer.

In some examples the apparatus further comprises a third printhead,wherein the controller is to cause the third printhead to deposit athird liquid which absorbs ultraviolet radiation onto the layer ofparticulate material, after the second printhead deposits the secondliquid. For example, the third liquid may be a liquid coloreddifferently to the second liquid. For example the second liquid may havea Cyan color, and the third liquid may have a Magenta color. Furtherprintheads may deposit further colors, such as Yellow and Black, therebyallowing a plurality of colors to be imparted to the object as it isbuilt layer-by-layer. In some examples, the second and third liquids aredeposited from different nozzles in the same printhead.

In other examples, however, the third printhead may be similar to thefirst printhead and the third liquid may be the same as the firstliquid. In certain examples the first and third printheads are arrangedat opposite ends of a printer carriage. For example, the first and thirdprintheads may be at opposite ends of the carriage with respect to adirection traveled by the printer cartridge during printing. Thus, thefirst liquid can be deposited by both the first and third printheadsallowing the print carriage to be used in two directions. The CMYKprintheads or nozzles may be located between the first and thirdprintheads. Thus, in examples where the first liquid and the thirdliquid are the same, the third printhead may be configured to depositthe third liquid after the UV-LED energy source has caused a portion ofthe particulate material to fully solidify.

In some examples the UV-LED energy source is a first UV-LED energysource, and the apparatus comprises a second UV-LED energy source,wherein the controller is to cause the second UV-LED energy source toirradiate the layer and therefore the first liquid, before the secondprinthead deposits the second liquid. Accordingly, a second UV-LEDenergy source may be used to pre-heat the first liquid rather than asingle UV-LED energy source being used for both pre-heating andsolidifying the particulate material. The second UV-LED energy sourcemay be located within the apparatus in a position more suited topreheating the liquid after it has been deposited. In some examples, thesecond UV-LED energy source comprises one or more UV-LEDs, for examplean array of UV-LEDs.

In some examples the first UV-LED energy source has a first peakwavelength and the second UV-LED energy source has a second peakwavelength, the first wavelength and the second wavelength beingdifferent to each other. This allows different wavelengths to be useddepending upon the function. For example, the first wavelength may bemore suited for solidifying the particulate material, and the secondwavelength more suited for pre-heating.

In one example, the second peak wavelength used for pre-heating isselected based on the first liquid and the first peak wavelength isselected based on the second liquid. In some examples the first peakwavelength is selected based on both the first and second liquids.

FIG. 1 shows an example three-dimensional printing apparatus 100. Thethree-dimensional printing apparatus 100 comprises a printhead 102. Theprinthead 102 is arranged to deposit a liquid 104, such as a liquid,upon a layer of particulate build material 106 that is received within abuild area, such as on platform 108. In some examples the build area andplatform 108 are separate from the printing apparatus 100. In thisexample, the build area and platform 108 are separate, but are presentin use. The particulate material may be, for example, a powderedsubstrate in the example of FIG. 1 . The printhead 102 may be moveablerelative to the material 106. In one case, the print head 102 may belocated in a moveable carriage located above the material 106. Theprinthead 102 may move in one, two or three directions over the material106, for example along the x-axis direction indicated in FIG. 1 , alonga y-axis, for example into and out of the page of FIG. 1 , and in someexamples vertically in the z-axis direction. In another case, theplatform 108 and material 106 may be moveable underneath a static printhead. Various combinations of approaches are possible.

In the example of FIG. 1 , the printhead comprises one or more nozzlesconfigured to deposit the liquid onto a portion 112 of the layer ofparticulate material 106. The ejection mechanism may be based onpiezo-electric or thermal elements. The three-dimensional printingapparatus 100 may have a resolution similar to that of a two-dimensionalprinting apparatus, for example 600 or 1200 dots per inch (DPI).

The particulate material 106 may be deposited within the build area by asubstrate supply mechanism 110. The supply mechanism 110 may beconfigured to supply at least one layer of particulate material 106 ontowhich the liquid 104 can be deposited. In some examples the supplymechanism 110 is separate and removable from the apparatus 100, and maybe present in use.

In the three-dimensional printing apparatus 100 of FIG. 1 , an objectmay be built up layer by layer. Each layer of material 106 may have athickness in the z-axis. In one case, this thickness may be between70-120 microns, although in other examples thicker or thinner layers maybe formed. The three-dimensional printing apparatus 100 is arranged tosolidify portions 112 of the material in each successive layer.

In one example, the liquid can be deposited within an addressable areaof a layer of build material. Accordingly, through the deposit ofmultiple droplets over successive layers, a three-dimensional object canbe built.

The apparatus 100 further comprises an UV-LED energy source 114. TheUV-LED energy source may comprise one or more UV-LEDS, such as an arrayof UV-LEDs, for example. Following application of the liquid 104, theUV-LED energy source 114 emits ultraviolet electromagnetic radiationover the layer 106. The liquid is also configured to absorb ultravioletradiation emitted by the UV-LED energy source 114. This radiation causesthe material to melt or sinter, and then fix or solidify upon cooling inthe regions where the liquid 104 was deposited. For example, the UV-LEDenergy source may irradiate the layer of material 106 withelectromagnetic radiation within a wavelength range, and because theliquid is an absorber of the specific UV wavelengths emitted by theUV-LED energy source 114, the liquid absorbs at least some of the energyand transfers at least some of the absorbed energy to the material inthe vicinity of the liquid. Regions which do not receive the liquid 104may not heat up sufficiently to melt and subsequently solidify. Toreduce the effect of neighbouring material solidifying in othernon-object areas, the UV wavelength can be selected so that it isefficiently absorbed by the liquid, but poorly absorbed by the drymaterial 106. In one example, the peak wavelength has a maximumintensity at a wavelength of between about 385 nm to about 405 nm,however other wavelengths may be suitable depending upon the liquid andparticulate material absorbances.

The apparatus may further comprise a controller 116. The controller 116can control the various components of the apparatus 100. The controller116 may comprise one or more processors for example. The controller 116may further comprise memory, to store instructions that when executed,cause the processor(s) to implement one or more methods. For example,the controller may control the printhead 102, the supply mechanism 110,the carriage, the UV-LED energy source 114 and movement of the platform108. The memory may be a non-transitory computer-readable storage mediumin some examples. The controller 116 may be connected directly orindirectly to the various components of the printing system 100 via oneor more communication paths 118, shown depicted as dashed lines. In someexamples, the various components each have their own controller whichmay operate independently of each other, or in cooperation.

In one example, the liquid 104 is colored. For example, the liquid maybe a colorant, such as a dye or pigment based ink. The liquid maytherefore comprise a colorant and/or a pigment. The colorants orpigments may themselves be the elements that enable the liquid to absorbthe ultraviolet radiation, however in some examples other properties ofthe liquid enable the liquid to absorb the radiation.

FIG. 2 shows another example three-dimensional printing apparatus 200that is substantially the same as apparatus 100, but further comprises asecond printhead 220 configured to deposit a second liquid 222. Thesecond printhead 220 is arranged adjacent to the first printhead 202 inthis example, although other arrangements are possible.

The three-dimensional printing apparatus 200 comprises a first printhead202. The first printhead 202 is arranged to deposit a first liquid 204upon a layer of particulate build material 206 that is received within abuild area, such as on platform 208. Similarly, the second printhead 220is arranged to deposit a second liquid 222 upon a layer of material 206.In one case, the first and second printheads 202, 220 are located in amoveable carriage 224 located above the platform 208. The carriage 324may move in one, two or three directions over the material 206. Inanother case, the platform 208 and material 206 may be moveableunderneath a static carriage 224. In some examples the first and secondprintheads 202, 220 are not located in a carriage 224. Variouscombinations of approaches are possible in different examples.

In the example of FIG. 2 , the first printhead 202 comprises one or morenozzles configured to deposit the first liquid 204 onto a portion 212 ofthe layer of particulate material 206. Similarly, the second printhead220 comprises one or more nozzles configured to deposit the secondliquid 222 onto a portion 212 of the layer of particulate material 206.In this example, both liquids are deposited within the same portion 212and at least partially overlap, however in some examples one of theliquids may be deposited within an area. In one example every portionreceives the first liquid, whereas in other examples some portionsreceive the second liquid.

The apparatus 200 further comprises an UV-LED energy source 214.

In one specific implementation, the apparatus 200 may be used to print acolored three-dimensional object. In order to achieve a good qualityprint, a white liquid may first be applied to particulate material 206upon which one or more other colored liquids are applied, such as Cyan,Magenta, Yellow and/or Black (CMYK), or other spot colors. The firstliquid may be colorless, however in one example the first liquid is awhite colored liquid, such as a dye. Thus, the white colored liquid hasno, or a low absorbance of visible light. The second liquid may be aliquid colorant, which is applied after the first liquid has beendeposited. In any case, both the first liquid 204 and the second liquid222 absorb ultraviolet radiation. In one particular example, the firstliquid is Contone-O.

In a first example, the first printhead 202 deposits the first liquid204, followed by the second printhead 220 depositing the second liquid222. Electromagnetic energy is applied by the UV-LED energy source tothe layer 206 and one or both liquids absorb the radiation, which causesthe material to melt or sinter, and then fix or solidify upon cooling inthe regions where the liquid 204 was deposited. For example, the UV-LEDenergy source may irradiate the layer of material 206 withelectromagnetic radiation within a wavelength range, and because theliquids are absorbers of UV, the liquids absorb the energy and transferthis energy to the material in the vicinity of the liquid. Regions witha low color density, i.e. regions with little or no second liquid 222will still solidify because of the presence of the first liquid 204.

The apparatus may further comprise a controller 216. The controller 216may control the various components of the apparatus 200 via one or morecommunication paths 218, as described for the example apparatus 100 inrelation to FIG. 1 . The controller 216 can control the ordering andtiming of when the first and second printheads 202, 220 deposit theirrespective liquids onto the layer of particulate material 206.

FIG. 3 shows another example three-dimensional printing apparatus 300that is substantially the same as apparatus 200, but further comprises athird printhead 320 configured to deposit a third liquid 328 upon alayer of material 306. The third printhead 326 is arranged adjacent tothe second printhead 320, such that the first printhead 302 and thethird printhead 326 are arranged at opposite ends of the print carriage324. Other arrangements are possible.

The three-dimensional printing apparatus 300 comprises a first printhead302. The first printhead 302 is arranged to deposit a first liquid 304upon a layer of particulate build material 306 that is received within abuild area, such as on platform 308. Similarly, the second printhead 320is arranged to deposit a second liquid 322 upon a layer of material 306.In one case, the first, second and third printheads 302, 320, 326 arelocated in a moveable carriage 324 located above the material 306. Thecarriage 324 may move in one, two or three directions over the material306. In another case, the platform 308 and material 306 may be moveableunderneath a static carriage 324. In some examples the first, second andthird printheads 302, 320 are not located in a carriage 324. Variouscombinations of approaches are possible.

In the example of FIG. 3 , the first printhead 302 comprises one or morenozzles configured to deposit the first liquid 304 onto a portion 312 ofthe layer of particulate material 306. Similarly, the second printhead320 comprises one or more nozzles configured to deposit the secondliquid 322 onto a portion 312 of the layer of particulate material 206.

The apparatus 300 further comprises an UV-LED energy source 314.

In one implementation, the apparatus 300 may be used to print a coloredthree-dimensional object. As described in relation to FIG. 2 , the firstliquid 304 may be a white colored liquid, such as a dye, and the secondliquid 322 may be another colored liquid, such as a pigment-based ink.Both the first liquid 304 and the second liquid 322 absorb ultravioletradiation. In one example the third printhead 326 is substantiallysimilar to the second printhead 320 except the third liquid is adifferent color to the second color. Thus the third liquid is also anabsorber of UV radiation. In one example, the first liquid may be white,the second liquid may be Cyan and the third color may be Magenta. Two ormore printheads may also be included for Yellow and Black. After thefirst, second and third liquids have been applied, the UV-LED energysource 314 may irradiate the layer of material 306 with electromagneticradiation to cause portions of the material to solidify where at leastone liquid has been applied. In one example, the second and thirdprintheads are a single entity, and the second and third liquids aredifferent, but are deposited from different nozzles within the singleprinthead.

However, in another implementation, the third printhead 326 issubstantially similar to the first printhead in that the third liquid328 deposited by the third printhead 326 is the same liquid as the firstliquid. For example, the third liquid may also be a white liquid. Byhaving two printheads dispensing the first liquid, the print carriage issymmetrical, and can thus be used to deposit the first liquid onto drymaterial 306 before applying a colored liquid from one or more otherprintheads. Accordingly, as the print carriage 324 moves over the layerof material 306 along the x-axis, the carriage is able to first depositthe white liquid regardless of which direction along the x-axis thecarriage is moving. Thus, in examples where the liquid deposited by thethird printhead 302 is the first liquid, the UV-LED energy source 314may irradiate the layer of material 306 with electromagnetic radiationafter the first and second printheads 302, 320 have deposited theirliquids, and before the third printhead 326 deposits the first liquidagain. Alternatively, the carriage 324 moves in the y-direction, abovemore dry material before the third printhead deposits the first liquid.

The apparatus may further comprise a controller 316. The controller 316may control the various components of the apparatus 300 via one or morecommunication paths 318, as described for the example apparatus 100 inrelation to FIG. 1 . The controller 316 can control the ordering andtiming of when the first, second and third printheads 302, 320, 326deposit their respective liquids onto the layer of particulate material206.

FIG. 4 shows another example three-dimensional printing apparatus 400that is substantially the same as apparatus 200, but further comprises asecond UV-LED energy source 430. The apparatus depicted in FIGS. 1 and 3may also comprise a second UV-LED energy source in certain examples.

As was described for FIG. 2 , the three-dimensional printing apparatus400 comprises a first printhead 402. The first printhead 402 is arrangedto deposit a first liquid 404 upon a layer of particulate build material406 that is received within a build area, such as on platform 408.Similarly, the second printhead 420 is arranged to deposit a secondliquid 422 upon a layer of material 406. Both the first liquid 404 andthe second liquid 422 are absorbers of ultraviolet radiation. In onecase, the first and second printheads 402, 420 are located in a moveablecarriage 424 located above the material 406. The carriage 424 may movein one, two or three directions over the material 406. In another case,the platform 408 and material 406 may be moveable underneath a staticcarriage 424. In some examples the first and second printheads 402, 420are not located in a carriage 224. Various combinations of approachesare possible.

The apparatus may further comprise a controller 416. The controller 416may control the various components of the apparatus 400 via one or morecommunication paths 418, as described for the example apparatus 100 inrelation to FIG. 1 . The controller 416 can control the ordering andtiming of when the first and second printheads 402, 420 deposit theirrespective liquids onto the layer of particulate material 406 and theordering and timing of when the first and second UV-LED energy sources414, 430 irradiate the particulate material 406.

In one example, the first printhead 402 deposits the first liquid 404,before the second printhead 420 deposits the second liquid 422. However,in contrast to the example apparatus 200 of FIG. 2 , the second UV-LEDenergy source 430 is to irradiate the layer of particulate material 406,and therefore the first liquid, before the second printhead 420 depositsthe second liquid 422. Thus, the second UV-LED energy source 430pre-heats the material. Following the pre-heating, the second liquid isdeposited, and finally the first UV-LED energy source 414 irradiates thelayer of particulate material 406, and therefore both the first andsecond liquids, to cause a portion of the material to solidify.

In some examples both the first and second UV-LED energy sources are thesame, and thus emit electromagnetic radiation having substantially thesame physical properties such as peak wavelength and spectral width. Inother examples however the first UV-LED energy source has a first peakwavelength and the second UV-LED energy source has a second peakwavelength, the first wavelength and the second wavelength beingdifferent to each other. Wavelengths and/or spectral widths can beselected depending upon their use. For example, certain wavelengthsand/or spectral widths may be more suited for pre-heating and otherwavelengths and/or spectral widths may be more suited for finally fusingand solidifying the material.

Pre-heating of the first liquid can also be achieved in apparatus wherethere is a single UV-LED energy source, such as in the examples of FIGS.1-3 . In this instance, the first UV-LED energy source can be used forboth pre-heating and finally fusing the material.

In some examples, the first UV-LED energy source is located on the printcarriage. Similarly, in apparatus comprising a second UV-LED energysource, one or both energy sources may be located on the print carriage.This allows the UV-LED energy source to move with the print carriage.FIG. 5 shows such an example.

FIG. 5 shows another example three-dimensional printing apparatus 500that is substantially the same as apparatus 300, but further comprises asecond UV-LED energy source 530. In addition, the first and secondUV-LED energy sources 514, 530 are located on the carriage. Each UV-LEDenergy source is arranged to heat the entire layer of material 506. Insome examples the first and second UV-LED energy sources are not locatedon the carriage.

As was described for FIG. 3 , the apparatus 500 comprises a firstprinthead 502, a second printhead 520 and a third printhead 526. Thefirst printhead 502 is arranged to deposit a first liquid 504 upon alayer of particulate build material 506 that is received within a buildarea, such as on platform 508. Similarly, the second printhead 520 isarranged to deposit a second liquid 522 upon the layer of material 506.Similarly, the third printhead 526 is arranged to deposit a third liquid528 upon the layer of material 506. In one case, the carriage 524 ismoveable in one, two or three directions over the material 506. Inanother case, the platform 508 and material 506 may be moveableunderneath a static carriage 524. Various combinations of approaches arepossible.

The apparatus 500 further comprises first and second UV-LED energysources 514, 530. In FIG. 5 , the first and third printheads 502, 526are arranged at opposite ends of the print carriage 524 and one or moresecond printheads 522 are located therebetween. Arranged adjacent to thefirst printhead 502 is the second UV-LED energy source 530, which itselfis arranged adjacent the second printhead 520. Arranged adjacent to thethird printhead 526 is the first UV-LED energy source 514, which itselfis arranged adjacent the second printhead 520. In this example, thefirst and third printheads 502, 526 are arranged to deposit the sameliquid.

In one implementation, the apparatus 500 may be used to print a coloredthree-dimensional object. As described in relation to FIG. 2 , the firstliquid 504, 528 may be a white colored liquid, such as a dye, and thesecond liquid 522 may be another colored liquid, such as a pigment-basedink. Both the first liquid 504, 528 and the second liquid 522 absorbultraviolet radiation.

In use, the print carriage 524 moves at least moves along thex-direction. At a particular time, the carriage is moving in thepositive x-direction, towards the right hand side of FIG. 5 . Thus, eachof the elements on the carriage are operated in sequence as the carriagemoves. For example, the first printhead 502 first deposits a firstliquid onto the particulate material 506. Next, the second UV-LED energysource 530 is to irradiate the layer of material 506 to pre-heat thematerial 506. Next, one or more second printheads 520 deposit coloredliquids to develop colors within the layer of material 506. Next, thefirst UV-LED energy source 514 irradiates the layer 506 to solidify thematerial in regions where the liquids have been deposited. At this time,the print carriage is located towards the right hand side of FIG. 5 .Next, the supply mechanism 510 deposits a subsequent layer of materialon top of the layer 506. The process can then repeat again, with thecarriage moving in the opposite direction, for example. Hence the thirdprinthead first deposits the first liquid onto the new layer ofmaterial.

In one example, each colored layer of particulate material is formed ontop of a previously formed white layer. This can be useful if thecolored layer has a coverage value of less than 100%. Alternating whiteand colored layers can be therefore created. For example, this can beachieved by initially forming a white layer, in which the white firstliquid is applied to a first layer of particulate material.Electromagnetic energy from a UV-LED energy source is then applied tothe first layer, which causes the first layer to fuse. The first layertherefore forms a white reflective layer upon which a subsequent full,or partial colored layer can be formed. For example, after forming thewhite first layer, a second layer of particulate material can be appliedon top of the first layer. The first liquid is then deposited in someregions, where color is not to be applied, and the second liquid isdeposited in other regions where color is to be applied. Electromagneticenergy from a UV-LED energy source is then applied to the second layer,which causes the second layer to fuse. The layer 506 shown in FIG. 5would therefore correspond to this second layer, and the first layerwould be located below layer 506. As mentioned, this technique can beused to create an object having less than a 100% color coverage. Forexample, a 50% cyan colored layer can be achieved in this way. This maybe useful when the colored liquids are to be deposited on a whitesurface and the particulate material itself is not pure white whenfused. In some examples, pre-heating the colored layer after depositingone of the liquids is optional.

The apparatus may further comprise a controller 516. The controller 516may control the various components of the apparatus 500 via one or morecommunication paths 518, as described for the example apparatus 100 inrelation to FIG. 1 . The controller 516 can control the ordering andtiming of when the printheads 502, 520, 526 deposit their respectiveliquids onto the layer of particulate material 506 and the ordering andtiming of when the first and second UV-LED energy sources 514, 530irradiate the particulate material 506.

In some examples, the controller is to cause a first printhead todeposit a first liquid which absorbs ultraviolet radiation onto a firstlayer of particulate material, and cause an UV-LED to irradiate thefirst layer of particulate material, after the first liquid has beendeposited onto the first layer of particulate material, thereby to heatthe first liquid and cause a portion of the particulate material tosolidify. In some examples the controller is further to cause a supplymechanism to form a second layer of particulate material and cause thefirst printhead to deposit the first liquid onto the second layer, andcause a second printhead to deposit a second liquid onto the secondlayer. The controller is further to cause an UV-LED to irradiate thesecond layer of particulate material thereby to heat the first andsecond liquid and cause a portion of the particulate material tosolidify.

In some examples, such as the systems described in FIGS. 1-5 , each ofUV-LEDs in a UV-LED array irradiate the layer of particulate material atsubstantially the same time. However, in other examples, the UV-LEDs inthe UV-LED array irradiate the layer sequentially, by applying energy ina scanning manner.

FIG. 6 shows an example dye absorption spectrum 602 for a first liquid,in this case Contone-O, a UV-LED emission spectrum with a maximumintensity emission at 385 nm, and an absorption spectrum 606 of PA-12,an example particulate material. PA-12 has an absorbance peak at around350 nm. In this example, therefore, most of the emitted UV energy willbe absorbed in the dye, and little energy will be absorbed by thematerial in regions where the dye has not been deposited. For example,around 70% of the energy incident on the dye will be absorbed by the dyeand less than 10% of the energy incident on the particulate materialwill be absorbed by the particulate material in regions where there isno dye. In certain instances, the energy that is absorbed by theparticulate material in regions where there is no dye is not sufficientto cause the material to melt and subsequently fuse. In this example,similar results may be achieved using Contone-O, PA-12 and a UV-LEDhaving a maximum intensity at a wavelength between about 385 nm to about405 nm.

In some examples the UV-LED energy source is to emit electromagneticenergy having a maximum intensity at a wavelength between about 350 nmto about 405 nm. Suitable first liquids may be used which have anabsorbance peak within this range. Wavelengths within this range may besufficiently far removed from the peak absorbance of PA-12, to reducethe likelihood of the dry particulate material from reaching its meltingtemperature.

It will be appreciated that the selected UV-LED wavelength is dependentupon the liquids being used and on the particulate material, so othersuitable wavelengths may be used that achieve the same, or similarresults.

In the example of FIG. 6 , the first liquid (dye) has an absorbance peakat about 385 nm, however in other examples other liquids may be usedwhich have absorbance peaks in the range of about 350 nm to about 420nm. Hence, suitable UV LEDs can be selected which emit radiation withinthis range. Due to practical limitations, such as cost, UV-LEDs may beselected which emit radiation in the range of 365 nm to 400 nm.

FIG. 7 shows the absorption spectrums of example yellow Y, magenta M,and cyan C pigment-based inks. Black colorant has substantially 100%absorption efficiency over this range. The output intensity of anexample UV-LED, in this example a 395 nm LED, over its spectral width isalso shown (with an arbitrary vertical scale), labeled UV LED. A 395 nmLED is an example of a readily available LED. Another such example is a405 nm LED. The spectral width of this example UV-LED is about 20 nm.Such a UV-LED energy source will be absorbed efficiently by all of thesecolorants. For example, at this wavelength Cyan will have approximatelya 95% absorbance efficiency, Magenta will have approximately a 75%absorbance efficiency, Yellow will have approximately a 100% absorbanceefficiency and Black will have approximately a 100% absorbanceefficiency. Similarly, as explained in FIG. 6 , a UV-LED with a maximumintensity at about 395 nm will also be efficiently absorbed byContone-O, having an absorbance efficiency of around 70% and will bepoorly absorbed by dry PA-12, having an absorbance efficiency of around10%.

FIG. 8 is a flow diagram showing a method 800. The method can beperformed by the example apparatus 100, 200, 300, 400, 500. At block 802the method comprises forming a layer of particulate material. At block804 the method comprises depositing a liquid which absorbs ultravioletradiation onto the layer of particulate material. At block 806 themethod comprises, after the liquid has been deposited onto the layer ofparticulate material, heating the liquid using an ultraviolet lightemitting diode energy source to cause a portion of the particulatematerial to solidify.

In some example methods, heating the liquid using an ultraviolet lightemitting diode energy source comprises irradiating the layer ofparticulate material with ultraviolet electromagnetic energy having aspectral width of about 5 nm to about 50 nm.

In some example methods, heating the liquid using an ultraviolet lightemitting diode energy source comprises irradiating the layer ofparticulate material with ultraviolet electromagnetic energy having amaximum intensity at a wavelength between about 200 nm to about 405 nm.

In some example methods, heating the liquid using an ultraviolet lightemitting diode energy source comprises irradiating the layer ofparticulate material with ultraviolet electromagnetic energy having amaximum intensity at a wavelength between about 385 nm to about 405 nm.

In some example methods, the liquid is a first liquid, and the methodfurther comprises heating the first liquid using an ultraviolet lightemitting diode energy source before depositing a second liquid, whereinthe second liquid absorbs ultraviolet radiation.

Certain system components and methods described herein may beimplemented by way of non-transitory computer program code that isstorable on a non-transitory storage medium. In some examples, thecontrollers may comprise a non-transitory computer readable storagemedium comprising a set of computer-readable instructions storedthereon. The controllers may further comprise one or more processors903. In some examples, control may be split or distributed between twoor more controllers which implement all or parts of the methodsdescribed herein.

FIG. 9 shows an example of such a non-transitory computer-readablestorage medium 900 comprising a set of computer readable instructions901 which, when executed by at least one processor 903, cause theprocessor(s) 903 to implement a method according to examples describedherein. The computer readable instructions 901 may be retrieved from amachine-readable media, e.g. any media that can contain, store, ormaintain programs and data for use by or in connection with aninstruction execution system. In this case, machine-readable media cancomprise any one of many physical media such as, for example,electronic, magnetic, optical, electromagnetic, or semiconductor media.More specific examples of suitable machine-readable media include, butare not limited to, a hard drive, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory, or aportable disc.

In an example, instructions 901 cause the processor 903 in a stackingsystem to, at block 902, form a layer of particulate material. At block904, the instructions 901 cause the processor 903 to deposit a liquidwhich absorbs ultraviolet radiation onto the layer of particulatematerial. At block 906, the instructions 901 cause the processor 903 to,after the liquid has been deposited onto the layer of particulatematerial, heat the liquid using an ultraviolet light emitting diodeenergy source, thereby to heat the liquid and cause a portion of theparticulate material to solidify. In some examples, the ultravioletlight emitting diode energy source emits electromagnetic energy having amaximum intensity at a wavelength of between about 200 nm to about 405nm.

The preceding description has been presented to illustrate and describeexamples of the principles described. This description is not intendedto be exhaustive or to limit these principles to any precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching. It is to be understood that any feature described inrelation to any one example may be used alone, or in combination withother features described, and may also be used in combination with anyfeatures of any other of the examples, or any combination of any otherof the examples.

What is claimed is:
 1. Apparatus to produce a three-dimensional object,the apparatus comprising: a controller; a first printhead; a secondprinthead to deposit colorant according to a desired coloring of theobject; and an ultraviolet light emitting diode energy source to emitelectromagnetic energy; wherein the controller is to: cause the firstprinthead to deposit a liquid which absorbs ultraviolet radiationemitted by the ultraviolet light emitting diode energy source onto alayer of particulate material; cause the ultraviolet light emittingdiode energy source to irradiate and preheat at least a portion of thelayer of particulate material, after the liquid has been deposited ontothe layer of particulate material; and cause the second printhead todeposit the colorant of the desired coloring on the preheated portion ofthe layer of particulate material.
 2. Apparatus according to claim 1,wherein the ultraviolet light emitting diode energy source is to emitultraviolet electromagnetic energy having a spectral width of about 5 nmto about 50 nm.
 3. Apparatus according to claim 1, wherein theultraviolet light emitting diode energy source is to emitelectromagnetic energy having a maximum intensity at a wavelengthbetween about 385 nm to about 405 nm.
 4. Apparatus according to claim 1,wherein the controller is to: cause the second printhead to deposit thecolorant comprising a second liquid which absorbs ultraviolet radiationemitted by the ultraviolet light emitting diode energy source after thefirst printhead deposits the first liquid.
 5. Apparatus according toclaim 4, wherein the first liquid deposited by the first printhead iswhite.
 6. Apparatus according to claim 4, the apparatus furthercomprising a third printhead, wherein the controller is to cause: thethird printhead to deposit a third liquid which absorbs ultravioletradiation emitted by the ultraviolet light emitting diode energy sourceonto the layer of particulate material, after the second printheaddeposits the second liquid.
 7. Apparatus according to claim 4, whereinthe ultraviolet light emitting diode energy source is a firstultraviolet light emitting diode energy source, the apparatuscomprising: a second ultraviolet light emitting diode energy source;wherein the controller is to cause the second ultraviolet light emittingdiode energy source to irradiate at least a portion of the layer ofparticulate material, before the second printhead deposits the secondliquid.
 8. Apparatus according to claim 7, wherein the first ultravioletlight emitting diode energy source has a first peak wavelength and thesecond ultraviolet light emitting diode energy source has a second peakwavelength, the first peak wavelength and the second peak wavelengthbeing different to each other.
 9. A method of producing athree-dimensional object, the method comprising: forming a layer ofparticulate material; depositing a liquid which absorbs ultravioletradiation onto the layer of particulate material to form a surface toreceive a desired coloring; after the liquid has been deposited onto thelayer of particulate material, heating the liquid using an ultravioletlight emitting diode energy source; and printing colorant of the desiredcoloring on the heated liquid and particulate layer.
 10. A methodaccording to claim 9, wherein heating the liquid using an ultravioletlight emitting diode energy source comprises irradiating at least aportion of the layer of particulate material with ultravioletelectromagnetic energy having a spectral width of about 5 nm to about 50nm.
 11. A method according to claim 9, wherein the ultraviolet lightemitting diode energy source emits electromagnetic energy having amaximum intensity at a wavelength between about 200 nm to about 405 nm.12. A method according to claim 9, wherein the colorant comprises asecond liquid, wherein the second liquid absorbs ultraviolet radiation.13. A method according to claim 9, further comprising heating the firstliquid, colorant and particulate material using a second ultravioletlight emitting diode energy source to fuse the particulate material intoa portion of the object having the desired coloring.
 14. Anon-transitory computer-readable storage medium storing instructionsthat, when executed by a processor, cause the processor, to: form alayer of particulate material; deposit a liquid which absorbsultraviolet radiation onto the layer of particulate material to form asurface to receive a desired coloring; after the liquid has beendeposited onto the layer of particulate material, heat the liquid usingan ultraviolet light emitting diode energy source; and printing colorantof the desired coloring on the heated liquid and particulate layer. 15.Apparatus according to claim 1, wherein the ultraviolet light emittingdiode energy source is to emit electromagnetic energy having a maximumintensity at a wavelength between about 200 nm to about 405 nm. 16.Apparatus according to claim 1, wherein the liquid comprises a whitedye.
 17. Apparatus according to claim 1, wherein the second printhead isto deposit Cyan, Yellow, Magenta and Black ink to form the desiredcoloring.
 18. Apparatus according to claim 1, further comprising amoveable carriage supporting the first printhead, second printhead andultraviolet light emitting diode energy source, the carriage alsosupporting a second ultraviolet light emitting diode energy source and athird printhead to deposit the liquid.
 19. Apparatus according to claim18, wherein the second printhead is disposed between the first and thirdprintheads so that, when the carriages moves in either direction, eitherthe first or third printhead will deposit the liquid on the particulatematerial, the liquid will be preheated by one of the energy sources, thedesired coloring then printed by the second printhead after thepreheating and the particular material and colored image then fused bythe other of the energy sources.
 20. Apparatus according to claim 1,further comprising a carriage moveable in two directions over theparticular material, wherein, along a direction of movement of thecarriage, the carriage supports the first printhead, the ultravioletlight emitting diode energy source, the second printhead, a secondultraviolet light emitting diode energy source and a third printhead todeposit the liquid.